The present invention relates generally to image forming equipment and is particularly directed to electrophotographic printers of the type which use a fuser hot roll to affix toner to a print media. The invention is specifically disclosed as a non-contact detack arrangement that separates the print media from the fuser hot roll, in which the detack fingers do not physically touch the hot roll.
In a typical electrophotographic printing process, toner is fused to the print media in the fusing station of the machine. The fusing station in desktop printers is normally composed of a heated, fluoropolymer-coated aluminum fusing roll, a soft elastomeric pressure roll, and a means to apply pressure between the two rolls. The combined action of heat, pressure, and dwell time in the nip formed between the two rolls causes the thermoplastic toner to soften and flow between the media fibers. Upon cooling the toner solidifies and is firmly affixed to the media.
During the fusing process, the toner can adhere to the fusing roll under certain conditions. In conventional printers the adhesion of the toner (and subsequently the media) to the fusing roll during the fusing process is alleviated by a media/roller separation mechanism that is in contact with the fusing roll. This separation mechanism (herein referred to as xe2x80x9ccontactxe2x80x9d detack fingers) consists of spring loaded fingers that are in contact with the fusing roll. FIG. 1 shows a conventional media/roller separation mechanism that is used in conventional Lexmark printer products. Please note that in FIG. 1 several fuser components are omitted for clarity.
In FIG. 1, a fuser hot roll is generally designated by the reference numeral 1, and is mounted into a fuser frame 3 by use of bearings 7. The print media (not shown) travels between a nip (not shown) between the fuser hot roll 1 and a pressure roll (not shown), and exits this nip through a second nip between a first exit roller 4 and a second exit roller 5. Exit rollers 4 and 5 are typically rotated at a somewhat greater linear velocity so as to produce a slight tension on the print media. This is also referred to as an xe2x80x9coverdrivexe2x80x9d configuration.
FIG. 1 also illustrates several contact detack finger subassemblies at the reference numerals 2. These xe2x80x9cfingersxe2x80x9d are better illustrated in FIG. 2, and make actual contact with the fuser hot roll 1.
FIG. 2 is another view of the conventional printer mechanism illustrated in FIG. 1. In FIG. 2, several fuser components are also omitted for clarity, including the fuser hot roll itself. The fuser bearing 7 is still illustrated, and is attached to the side bracket of the fuser frame 3. The pressure roll (sometimes referred to as a xe2x80x9cbackup rollxe2x80x9d) is generally designated at the reference numeral 8. The contact detack finger subassemblies 2 are shown in greater detail in FIG. 2, and the actual finger extension of these subassemblies 2 is illustrated at the reference numeral 6. As can be seen, the extension at 6 is the actual xe2x80x9cfingerxe2x80x9d or structure that makes contact via a spring-loaded mechanism with the fuser hot roll.
Although the contact detack fingers 6 accomplish their original design intent of stripping media off of the fusing roll 1, their frictional contact design has many disadvantages, namely fuser roll wear as well as acting as a toner collection site. As the fuser gets late in life, the frictional contact of the detack fingers 6 will wear the fuser roll 1 in the contact areas such that aluminum becomes exposed on the fluoropolymer coated fusing roll 1. The exposed aluminum will cause a print defect (e.g., vertical streaking), because toner has a tendency to stick to the exposed aluminum of the fusing roll. The detack fingers 6 also act as a collection site for unfused toner (because the fusing process is not 100% efficient and some toner stays on the fusing roll and not the media). The buildup of toner on the contact detack fingers can at times cause a very blunt tip of the conventional detack finger 6 thereby defeating the original design intent. The toner buildup can result in unnecessary fuser jams, or in toner being deposited onto the page after a threshold of toner has been accumulated on the detack tip, and then is released.
It would be an advantage to alleviate the faults caused by the conventional contact-type system of detack fingers by replacing these contact-type fingers with a non-contact system that nevertheless separates the print media from the fuser hot roll.
Accordingly, it is an advantage of the present invention to provide a fuser hot roll for an electrophotographic printer that does not use contact-type detack fingers, but instead uses a non-contact detack finger system that involves tight clearances that are maintained between a fuser hot roll and the non-contact detack fingers.
It is another advantage of the present invention to provide a set of non-contact detack fingers that are spaced-apart from the fuser hot roll by accurately controlling the top margin of the print media in conjunction with the non-contact detack clearance, which both reduces the cost of the printer fuser subassembly, and also creates a system that is more reliable by helping to avoid problems such as degraded print quality when the fuser becomes old, and also avoids jams that otherwise may occur with conventional contact detack fingers that have a buildup of toner.
It is a further advantage of the present invention to provide an electrophotographic (EP) printer with a non-contact detack finger system, in which a relatively tight locational/tolerance control of a non-contact detack housing is improved by use of a straightening rod and a locating technique that guarantees that a specified maximum clearance specification is not exceeded.
Additional advantages and other novel features of the invention will be set forth in part in the description that follows and in part will become apparent to those skilled in the art upon examination of the following or may be learned with the practice of the invention.
To achieve the foregoing and other advantages, and in accordance with one aspect of the present invention, an image forming fuser apparatus is provided, which comprises: a fuser hot roll and a pressure roll, wherein the fuser hot roll and the pressure roll form a nip therebetween; and a detack structure that is spaced-apart from the fuser hot roll, the detack structure comprising at least one extension proximal to the fuser hot roll such that a clearance gap is formed between the at least one proximal extension and the fuser hot roll; wherein the detack structure is positioned so as to ensure separation of a print media from the fuser hot roll after the print media travels through the nip, by use of the at least one proximal extension.
In accordance with another aspect of the present invention, an image forming fuser apparatus is provided, comprising: a fuser hot roll and a pressure roll, wherein the fuser hot roll and the pressure roll form a nip therebetween; and a detack structure that is spaced-apart from the fuser hot roll, such that a clearance gap is formed therebetween; wherein the detack structure is positioned such that the clearance gap exhibits a predetermined maximum distance, thereby ensuring separation of a print media from the fuser hot roll after the print media travels through the nip.
In accordance with yet another aspect of the present invention, a method for separating a print media from a fuser hot roll in an image forming apparatus is provided, in which the method comprises the following steps: providing a fuser hot roll and a pressure roll, wherein the fuser hot roll and the pressure roll form a nip therebetween; directing a print media through the nip while rotating the fuser hot roll and the pressure roll; and separating the print media from the fuser hot roll by use of a non-contact detack structure, while maintaining a clearance gap within a predetermined maximum distance between the non-contact detack and the fuser hot roll.
Still other advantages of the present invention will become apparent to those skilled in this art from the following description and drawings wherein there is described and shown a preferred embodiment of this invention in one of the best modes contemplated for carrying out the invention. As will be realized, the invention is capable of other different embodiments, and its several details are capable of modification in various, obvious aspects all without departing from the invention. Accordingly, the drawings and descriptions will be regarded as illustrative in nature and not as restrictive.